Irrigation Requirement of Crop

Irrigation requirement of crops id the quantity of water, exclusive of rainfall, required by a crop in a given time period for their normal growth under filed condition. It includes evapotranspiration not met by the rainfall, it also includes surface run off and percolation losses 

Consumptive Irrigation Requirement (CRI) :

CRI is the amount of irrigation water that is required in order to meet the evapotranspiration (consumptive use) needs of a crop during its full growth. So, nothing but the consumptive use itself, but exclusive of effective precipitation, stored soil moisture or ground water.

When the last two are ignored, then we can write  

CRI = Cu - Re

Where,

Cu = Consumptive use of water

Re = Effective rainfall during growth period of crop

Net Irrigation Requirement (NIR) :

NIR is the amount of irrigation water required to be delivered at the field to meet the evapotranspiration needs of crop as well as other needs like leaching, presowing requirements etc.

NIR = CIR + LR + PSR

Where,

LR = Leaching requirement 

PSR = Presowing requirement 

Field Irrigation Requirement (FIR) :

FIR is the amount of water required to meet the NIR plus the amount of water lost as surface runoff and deep percolation.

Where,

ᶯa  = Water application efficiency

Gross Irrigation Requirement (GIR) :

GIR is the amount of water required to meet the FIR plus the amount of irrigation water lost in conveyance through canal system by evaporation and seepage.

 

Where,

ᶯa  = Water conveyance efficiency 

Irrigation Efficiencies

In more mathematical or scientific terms, it is a measure of the extent to which input is well used for an intended task or function (output).

for irrigation in general, 

Different types of Irrigation Efficiencies,

• Water Conveyance Efficiency (ղc) 

It includes losses which occurs in conveyance from point of diversion into canal system to the fields.

• Water Application Efficiency (ղa) 

It includes losses such as runoff from the field and deep percolation.

• Water Use Efficiency (ղu)

It includes water required for leaching.

• Water Distribution Efficiency (ղd)

Where,

y = average numerical deviation in depth of water stored

d = average depth of water stored in the root zone during irrigation

Higher is the water distribution efficiency better is the crop response.

• Water Storage Efficiency (ղs)

Wn = F.C. - Available moisture in the soil prior to irrigation,

Duty and Delta

Duty (D): It is defined as the area of the land irrigated by a unit discharge of water flowing continuously for the duration of the base period of the crop, it is denoted by D. It is measured in hectares/m3/s. Duty is essential while designing the physical structure of water storage and conveyed system.

Factors' Affecting Duty of Water:

• Type of Crop
• Type of Soil
• Climatic Condition
• Method of Irrigation

Delta (Δ): Each crop requires a certain amount of water after a certain fixed interval of time, Delta is the total depth of water in centimetre required by a crop to come to maturity.

Relation Between Duty and Delta:

Let consider a crop of base period B days, to this crop 1 cumec of water is applied for B days

then,

V= 1 x (B x 24 x 60 x 60)

 = 86400 B cubic meter

Let V cubic meters of water mature D hectare of land

D hectare of land = D x 10000 Sq meter

Where,

D = Duty of water on the field

Δ = Delta, depth of water supplied to filed

B = Base period of crop in days

Crop Planning and Agricultural Practices

 Kharif Crops:

Rabi Crops: